Japanese Patent No. 3597069, titled “Thermal Infrared Array Sensor for Detecting Plurality of Infrared Wavelength Band”, describes a dual-wavelength uncooled thermal infrared array sensor. FIG. 5 to FIG. 9 show examples of the sensor described therein. FIG. 5 is an exemplary perspective diagram of a bolometer-type infrared array sensor that detects two infrared wavelength ranges, where two types of pixels that constitute the array are exemplarily shown.
According to the examples described in Japanese Patent No. 3597069, the thermal infrared array sensor that detects two infrared wavelength ranges is, as shown in FIG. 5, formed of a Si readout integrated circuit substrate 4 that has a readout integrated circuit and a perfect reflection film, and an upper layer member having a thermal insulation structure constituted by a diaphragm 2 that is supported by a beam 3 extending from the Si readout integrated circuit substrate 4 to have a gap from the substrate 4. It is possible to make such a thermal infrared array sensor capable of detecting infrared rays of different wavelength ranges, by using different multilayer structures or different thin film materials for the diaphragms 2 of adjoining pixels, or by varying from pixel to pixel the interval between the upper layer member and the perfect reflection film on the Si readout integrated circuit substrate 4.
FIG. 6 shows the first example described in Japanese Patent No. 3597069. The diaphragm 102 of a pixel is formed of a bolometer material thin film 105 made of vanadium oxide transmissive to infrared, and protective films 106 or protective films 107.
The protective films 106 of the pixel of the section A-A′ are SiN films and absorb infrared rays in the wavelength range of 8 to 14 μm. A high infrared absorption rate is achieved by the perfect reflection film 108 on the Si readout integrated circuit substrate 109 reflecting an incident infrared ray 1 toward the diaphragm 102.
In this case, the cavity 110 may have any dimension as long as the diaphragm 2 is separate from the perfect reflection film 108. Meanwhile, the protective films 107 of the other pixel shown by the section B-B′ are made of SiO2, which is almost transmissive to infrared. In order for infrared to be absorbed, an infrared absorptive thin film 111, which is impedance-matched to the vacuum, is formed on the upper surface of the diaphragm. The interval between the infrared absorptive thin film 111 and the perfect reflection film 108 is adjusted to 1 μm optically, such that infrared rays in the wavelength range of 3 to 5 μm are mainly absorbed into the infrared absorptive thin film 111 due to an optical interference that occurs between the infrared absorptive thin film 111 and the perfect reflection film 108.
Infrared rays absorbed in this manner are transformed to heat and change the temperature of the diaphragm. This in turn changes the resistance of the bolometer inside the diaphragm, and the resistance change is converted into an electric signal, which is signal-processed and turned into an image. It is possible to detect infrared rays in two wavelength ranges by forming an infrared array sensor by disposing pixels of the A-A′ section and of the B-B′ section in a desired arrangement or giving pixels of the B-B′ section different cavity lengths.
FIG. 7 shows the second example described in Japanese Patent No. 3597069. The diaphragm 112 of a pixel is formed of a bolometer material thin film 113 made of vanadium oxide transmissive to infrared, and protective films 114 or protective films 115. The protective films 114 and the protective films 115 are made of SiO2 that is almost transmissive to infrared.
An infrared absorptive thin film 117, which is impedance-matched to the vacuum, is formed on the upper surface of the diaphragm. In the pixel of the section A-A′, the interval between the infrared absorptive thin film 117 and the perfect reflection film 116 is adjusted to approximately 2.5 μm optically such that infrared rays in the wavelength range of 8 to 14 μm are absorbed due to an optical interference that occurs between the infrared absorptive thin film 117 and the perfect reflection film 116. Actually, the thickness of the SiO2 protective films is 500 nm and the cavity length (the dimension of the cavity 119) is 1.8 μm. Meanwhile, in the pixel of the section B-B′, the interval between the infrared absorptive thin film 117 and the perfect reflection film 116 is adjusted to approximately 1 μm optically such that infrared rays in the wavelength range of 3 to 5 μm are mainly absorbed. Actually, the thickness of the SiO2 protective films is 500 nm and the cavity length (the dimension of the cavity 120) is 0.3 μm.
It is possible to detect infrared rays in two wavelength ranges by forming an infrared array sensor by disposing sensors having different cavity lengths in a desired arrangement.
FIG. 8 shows the third example described in Japanese Patent No. 3597069. The diaphragm 121 of a pixel is formed of a metal bolometer material thin film 122 made of a metal thin film such as that of Ti having a thickness of 100 nm and infrared-reflective, a protective film 123 or a protective film 124, and a protective film 125. The protective film 123 and the protective film 124 are made of SiO2 that is almost transmissive to infrared.
An infrared absorptive thin film 126, which is impedance-matched to the vacuum, is formed on the upper surface of the diaphragm 121. In the pixel of the section A-A′, the thickness of the protective film 123 on the metal bolometer material thin film 122 is adjusted to approximately 2.5 μm optically such that infrared rays in the wavelength range of 8 to 14 μm are absorbed due to an optical interference that occurs between the infrared absorptive thin film 126 and the metal bolometer material thin film 122. Actually, the thickness of the SiO2 protective film is 1.6 μm. Meanwhile, in the pixel of the section B-B′, the thickness of the protective film 124 is adjusted to 1 μm optically such that infrared rays in the wavelength range of 3 to 5 μm are mainly absorbed. The thickness of the SiO2 protective film is 0.6 μm.
In this manner, it is possible to detect infrared rays in two wavelength ranges by forming an infrared array sensor by disposing, in a desired arrangement, sensors whose protective film, which is between the infrared absorptive thin film and the metal bolometer material thin film, has a thickness different from that of the protective film of other sensors.
FIG. 9 shows the fourth example described in Japanese Patent No. 3597069. As well as the third example, the diaphragm 130 of a pixel is formed of a metal bolometer material thin film 131 made of a metal thin film such as that of Ti and infrared-reflective. However, the difference lies in the combination of the material of the upper protective film of the diaphragm 130 and the infrared absorptive thin film. The diaphragm 130 of a pixel is formed of the metal bolometer material thin film 131 having a thickness of 100 nm and being infrared-reflective, and a protective film 132 or a protective film 133, and a protective film 135.
In the pixel of the section A-A′, the protective film 132 is a SiN film that absorbs infrared rays in the wavelength range of 8 to 14 μm. A high infrared absorption rate is achieved by the metal bolometer material thin film 131 reflecting an incident infrared ray 1 toward the protective film 132. Meanwhile, in the pixel of the section B-B′, the protective film 133 is made of SiO2 that is almost transmissive to infrared. An infrared absorptive thin film 134, which is impedance-matched to the vacuum, is formed on the upper surface of the diaphragm 130. The interval between the infrared absorptive thin film 134 and the metal bolometer material thin film 131 is adjusted to 1 μm optically such that infrared rays in the wavelength range of 3 to 5 μm are mainly absorbed due to an optical interference that occurs between the infrared absorptive thin film 134 and the metal bolometer material thin film 131. The thickness of the SiO2 protective film is 0.7 μm. Note that in this example, it does not matter whether the protective film 135 beneath the metal bolometer material thin film 131 is made of SiN or SiO2. The dimension of the cavity 136 may be any as long as the diaphragm 130 is separate from the Si readout integrated circuit substrate 137.
In this manner, it is possible to detect infrared rays in two wavelength ranges, by forming an infrared array sensor by disposing, in a desired arrangement, pixels having no infrared absorptive thin film but using an infrared absorptive protective film and pixels in which a metal bolometer material thin film and an infrared absorptive thin film are combined.